In 895, Rodulf took the castle of Saint-Quentin, expelling the unnamed son of Theodoricus. This made him master and Count of Vermandois (of which Saint-Quentin was the principal stronghold). Expelled in the next year by king Eudes, Rodulf continued to ravage possessions of the abbacy of Saint-Quentin until he was killed in battle with his third cousin Count Heribert I on 28 June 896. It was on Rodulf's defeat that Heribert obtained the region of Vermandois which gave Heribert's family the name by which it is now commonly known.
The claim that Rodulf was count of Cambrai does not appear in sources until the twelfth century, and is based on confusion with his kinsman Raoul de Gouy, father of the Raoul who was the historical prototype of the Raoul de Cambrai of romance (and an enemy of the sons of Heribert II of Vermandois, which no doubt helped to contribute to the confusion between the two).